Typical trucks with vacuum tanks (hereinafter referred to as “vacuum trucks”) consist of a cylindrical tank of sufficient construction to withstand a typical external pressure of 15 psi and an internal pressure from 15 psi for non-code tanks to 35 psi for U.S. Department of Transport (DOT)/Transport Canada (TC) 407/412 certified pressure vessels. The tanks are attached to a vacuum pump that may consist of a hydraulically driven air or liquid-cooled vane pump or a much larger, more powerful positive displacement blower or liquid ring vacuum pump.
The tanks on vacuum trucks are typically attached at their rear sides to a pivot or hinge-point at the rear of the truck, about which they are pivoted by a hydraulic dump cylinder operably coupled to the front of the tank (i.e., that end of the tank facing the front of the truck). In this manner, a hatch or door on the rear of the tank can be opened, the tank can be propelled upward at its front end so as to pivot about the pivot-point, and the contents of the tank, previously drawn into the tank by an attached vacuum system, can be discharged to the rear of the truck.
Vacuum trucks are usually subjected to road and bridge axle weight restrictions, and often are not able to take full advantage of the allowable gross weight over the front axle of the truck chassis. Front axles are typically permitted to bear an over-axle weight of 20,000 lbs, while rear axles are typically subjected to restrictions of 32,000 lbs or 40,000 lbs, depending on the jurisdiction. In jurisdictions where the lesser weight restriction is imposed, the typical payload for current vacuum trucks is approximately 15,000 lbs with the rear axles bearing their maximum allowable gross weight of 32,000 lbs and the front axle bearing only approximately 14,500 lbs of a possible 20,000 lbs of allowable over-axle weight. Where local laws allow the heavier rear axle rating, the typical payload increases to approximately 23,000 lbs, with the rear axles bearing their maximum allowable gross weight of 40,000 lbs and the front axle bearing only approximately 15,000 lbs of a possible 20,000 lbs of allowable over-axle weight.
The inability to transfer payload weight to the front axle, in order to scale the truck to its maximum capacity, severely limits the amount of material that can be loaded into the tank and legally hauled over roads and consequently, restricts profitability for the operator.
Further, while a vacuum tank is usually secured to a frame of the truck at the rear of the tank by a hinged connection, typically, the front of the tank simply rests on the frame with only the hydraulic dump cylinder holding down the front end. In some jurisdictions, this arrangement has been determined to be insufficient for securing the tank to the truck in the event of a rollover incident, and as such, regulations have come into effect requiring that all DOT/TC 407/412 cargo tanks certified for hauling hazardous waste incorporate a front tank hold-down.
Furthermore, traditional DOT/TC 407/412 vacuum trucks require that the rear bumper extend rearward from the truck, past the rear valves by a prescribed distance to provide crash protection for the rear valves in the event of a rear-end collision. This typically results in the contents of the tank being dumped onto the bumper, requiring operators to engage in the unsavoury and laborious task of manually cleaning the rear crash protection bumper prior to travelling on the roads. Additionally, hydraulic vibrators are often utilized on the bottom of the tank shell to assist in off-loading stubborn solid or semi-solid residue left in the tank.
Additional difficulties with existing systems may be appreciated in view of the detailed description below.